Note: Do not rely on this information. It is very old.
Januarius, St. (San Gennaro), the patron saint of Naples, was Bishop of Benevento at the end of the 3rd century. According to the Roman Breviary he suffered martyrdom under Diocletian at Pozzuoli in 305. His body was then taken to Naples, where some of his blood was preserved in a phial. It is supposed to liquefy on his anniversary (September 19), and two other days in the year, when it is carried in procession to be adored by the people. On the occurrence of any public calamity resort is also had to the miracle, which is even thought to counteract the eruptions of Vesuvius.